1. Field of the Invention
The present invention relates to an ultrasonic probe that is connected to an ultrasonic diagnostic instrument so as to transmit and receive ultrasonic waves to and from a sample.
2. Description of the Related Art
An ultrasonic probe is a device that is used for imaging the internal state of a sample by irradiating ultrasonic waves toward the sample and receiving a wave reflected from an interface having different acoustic impedance in the sample. Such ultrasonic probe is employed to, for example, an ultrasonic diagnostic instrument that inspects the interior of a human body.
The ultrasonic probe in the related art is configured of a piezoelectric vibrator, an acoustic matching layer disposed at a front surface of the piezoelectric vibrator, a backing material disposed at a rear surface of the piezoelectric vibrator, and a flexible printed circuit (FPC) connected to the piezoelectric vibrator. The piezoelectric vibrator includes earth electrode and signal electrode each connected to the front surface and the rear surface thereof. The piezoelectric vibrator generates the ultrasonic waves for scanning the sample on the basis of the voltage applied from the earth electrode and the signal electrode.
By this way, two methods are mainly used for the connection between the piezoelectric vibrator and the flexible printed circuit.
As a first technique, by drawing out the earth electrode into the rear surface of the piezoelectric vibrator, earth wiring of the piezoelectric vibrator is connected to the flexible printed circuit at the rear surface of the piezoelectric vibrator through a portion of the earth electrode drawn out into the rear surface of the piezoelectric vibrator (see, for example, JP-A-11-151239).
As a second technique, by forming a plating electrode on the entire surface of the acoustic matching layer, the earth wiring of the piezoelectric vibrator is connected to the flexible printed circuit at the front surface of the piezoelectric vibrator through the plating electrode. The acoustic matching layer having conductive property may be used. In this case, the plating electrode is unnecessary.
In addition, in both of the first and second techniques, the signal electrode of the piezoelectric vibrator and the flexible printed circuit is connected to each other at the rear surface of the piezoelectric vibrator.
By the way, in the first technique, the wiring between the earth electrode of the piezoelectric vibrator and the flexible printed circuit is electrically connected by a soldering process. For this reason, a piezoelectric material used in the piezoelectric vibrator is likely to be deteriorated by the influence of heat.
In addition, in the first technique, a notched portion is formed at the side of the packing material. The flexible printed circuit is inserted into the notched portion. For this reason, the piezoelectric vibrator is floating in the notched portion. As a result, during the joint of the piezoelectric vibrator and the packing material, if the piezoelectric vibrator is pressurized against the packing material, biased pressurization is applied to the piezoelectric vibrator. Therefore, the piezoelectric vibrator may be cracked.
Furthermore, in the first technique, the earth electrode of the piezoelectric vibrator and the flexible printed circuit are connected to each other at one location. For this reason, the electric joint reliability between the earth electrode of the piezoelectric vibrator and the flexible printed circuit is low.
Further, in the second technique, the metal having high acoustic impedance is used as the plating electrode formed on the surface of the acoustic matching layer. For this reason, the conditions of the acoustic matching fall into disorder by the plating electrode existing in a propagation path of the ultrasonic waves. Therefore, acoustic characteristics may be decreased.
Furthermore, in the second technique, since the acoustic matching layer having the conductive property DOES not necessarily have the acoustic impedance of the desire, sufficient acoustic matching conditions may not be obtained by the restriction of materials.